In the manufacture of circuit boards or cards, a circuit board is placed in a printer. A stencil is secured over the circuit board and a squeegee blade draws a solder paste over the stencil. This forms a pattern which becomes the conductive pattern of the circuit board.
As would be expected, after being used for some time the squeegee blades must be replaced, usually because of wear but also because of damage. In state of the art holders for squeegee blades, such as shown in FIG. 1, a prior art holder 10 is characterized by a stepped surface 14, a squeegee blade 16 having a pair of holes 18, a clamping bar 20 and a pair of threaded fasteners 22. The clamping bar secures the blade 16 to the holder 10. Typically, several fasteners, i.e. 10, are used. Here, only two are shown for clarity.
When the squeegee blade of FIG. 1 must be replaced all the threaded fasteners must be completely removed to release the squeegee blade. When the squeegee holder is open and the parts are separated, solder paste enters onto the surfaces of the holder and clamping bar. If the solder paste is not removed, when the holder is reassembled, the clamping force is reduced because of the presence of the solder paste. Another problem is that solder paste flows on the stepped surface and in the open tapped holes, further complicating blade replacement and most importantly reducing the accuracy of the blade position. It would appear logical that if a squeegee blade is to be replaced that the entire squeegee holder would be disassembled, cleaned and reassembled. In practice, this does not usually occur because it requires considerable time.
The squeegee holder embodied in the present invention does not require total disassembly of the squeegee holder. The squeegee holder is tolerant of paste contamination and incorporates a self-wiping action to insure that the new squeegee blade is clamped accurately to the holder.
Broadly the invention comprises a clamping assembly which is adapted to be secured to a solder paste applicator. The assembly comprises a holder which is characterized by two bearing surfaces, a first bearing surface and a second bearing surface. The second bearing surface has formed therein a pair of tapped holes, adapted to receive threaded fasteners, and a pair of holes adapted to have registration pins received therein. A clamping bar is adapted for mating engagement with the holder and has two pairs of holes in registration with the holes formed in the holder. The first pair of holes are in register with the tapped holes and threaded fasteners pass therethrough to secure the squeegee blade between the holder and the clamping bar. In practice, there would be several pairs of holes, only two pair are shown for clarity.
The other pair of holes are in register with the registration posts such as pins which pass through the holes. The registration pins locate the squeegee blade.
The first bearing surface is offset from the second bearing surface by a stepped surface. When assembled the clamping bar defines a recess with the second bearing surface and the stepped surface. When a new squeegee blade is clamped in place excess solder flows into the recess ensuring the blade is accurately aligned.